With a combination of analytical techniques, we can determine or confirm the molecular structure for a chemical entity. These techniques include mass spectrometry, NMR spectroscopy, infrared spectroscopy, elemental analysis and single crystal X-ray diffraction. We combine these techniques to address complex structural problems.
Mass spectrometry (MS) is the preferred technique to determine molecular weight and fragmentation data to support structure elucidation. The use of LC-MS enables the collection of structural data for many components in a complex mixture. We can use mass spectrometry to further characterize impurities observed using the LC procedure. The LC-MS data can be collected using different ionization techniques depending upon the nature of the sample. We can perform LC-MS, LC-MS/MS and LC-MS/MS/MS analyses using a linear ion trap instrument. The mass spectrometry data can be used for both quantitative and qualitative purposes.
We use high-resolution 1D and 2D NMR spectroscopy to determine the atomic connectivity and structural conformation of molecules in solution. Both 1H and 13C NMR spectroscopy provide detailed information about molecules. Various 2D proton NMR correlation experiments, such as COSY, TOCSY and NOESY, enable the determination of the relative locations of protons or the conformation of a molecule in solution. We also can conduct additional 2D proton-carbon NMR correlation experiments such as HMQC, HSQC and HMBC to connect the carbon backbone of complex molecules.
These NMR techniques are used to determine the assignments of all resonances for a molecule, and knowledge of the relative position of each nucleus permits the determination of the molecular conformation in solution. We can perform variable temperature, multinuclear and gradient-selected NMR analyses. Quantitative and qualitative data can be obtained using NMR spectroscopy.
Single Crystal X-Ray Diffraction
We use single crystal X-ray diffraction analysis to determine the dimensions of the unit cell and atomic coordinates, using this information to:
- Confirm the chemical structure of an API
- Unambiguously determine the absolute configuration of all stereocenters in a molecule
- Determine if the crystalline phase is a neat phase (pure API) or if it is a multicomponent crystal such as a hydrate or solvate
- Determine the stoichiometric ratio of components for salts, cocrystals, hydrates and solvates
- Uniquely identify forms and unravel the form landscape of polymorphic compounds
We use an in-house Rigaku SuperNova diffractometer equipped with a copper anode microfocus sealed X-ray tube and a Dectris Pilatus3 R 200K hybrid pixel array detector. The calculated powder X-ray pattern is generated from the determined crystal structure as a reference X-ray powder diffraction (XRPD) pattern for that particular form. This pattern can also be compared to the as-received powder material XRPD to assess the purity of the bulk material and confirm its form.